In a process of manufacturing semiconductor devices, a silicon wafer having a predetermined circuit pattern is diced into individual chips with a rotating round blade. A common way during the process involves bonding the silicon wafer to an adhesive film, dicing the silicon wafer into individual chips, stretching the adhesive film in lateral and longitudinal directions to expand the chip-to-chip distance, and picking up the chips (see Patent Literature 1). In recent years, laser ablation dicing of semiconductor substrates has attract attention because this dicing technique can process the substrates with high precision without thermal damaging compared to blade dicing. A proposed process in this technique involves fixing a work onto a dicing sheet and dicing the work with laser light (refer to PTL 2).
A manufacturing process of light emitting diodes (LEDs) using materials such as sapphire, gallium and arsenic yields individual chips of several hundred micrometers in size and therefore requires expansion of the chip-to-chip distance through sufficient stretching of an adhesive dicing film. A disadvantage of LED substrates that are fragile compared to silicon is that the dice are subjected to chipping during the conventional blade dicing. There has been a demand in the art for an expandable dicing substrate that is suitable for laser ablation dicing—a technique that is less damaging to substrates—and provides less contamination and sufficient expandability.
A requirement for an expandable dicing substrate is uniform stretching of the entire substrate without necking during a stretching operation. Necking results in partial expansion at the peripheries of the film with insufficient expansion in a central region of the film, and thus insufficient separation of chips in the central region. A commonly used expandable dicing substrate is soft vinyl chloride which barely undergoes necking (see, e.g., Patent Literature 3). A disadvantage of the expandable dicing substrate is contamination of the wafer by transfer of plasticizers contained in soft vinyl chloride through the adhesive layer (see Patent Literature 4). An expandable substrate composed of plasticizer-free thermoplastic polyolefin has been proposed as a substitution for vinyl chloride. Unfortunately, such an expandable substrate exhibits poor expansion and significant necking compared to vinyl chloride, resulting in an insufficient chip-to-chip distance, although it can reduce contamination of wafers.
Patent Literature 1 discloses a dicing film including a substrate and an adhesive layer, the substrate being composed of a thermoplastic resin having rubber elasticity and an ethylenic resin. A possible concern of the dicing film is necking, despite reduced contamination of a wafer.
Patent Literature 5 discloses a dicing film including an expandable substrate of a terpolymer (ionomer resin) composed of ethylene, acrylic acid, and alkyl acrylate ester as components.
Patent Literature 6 discloses a dicing film including an expandable substrate that is composed of a semi-compatible or non-compatible polymer blend containing a highly crystalline olefinic resin and a lowly crystalline olefin resin and that barely generates linty dust during dicing. Exemplified lowly crystalline olefinic resins are low-density polyethylene, random polypropylene copolymer, and ethylene-vinyl acetate copolymer.
Patent Literatures 7 to 9 each disclose a dicing film including an expandable substrate that is composed of propylene and ethylene, and/or α-olefinic thermoplastic elastomer having four to eight carbon atoms and that barely generates linty dust during dicing. According to the description, the α-olefinic thermoplastic elastomer may contain additives such as low-density polyethylene, polypropylene, polybutene, and polyesters.